Home > Misc. > 8878 Rechargeable Battery Box & 8887 Transformer

8878 Rechargeable Battery Box & 8887 Transformer

Overview of the new rechargeable Power Functions battery box along with its dedicated transformer.

The Lego company rarely releases new battery boxes, and a rechargeable battery is something entirely new. So far the battery boxes have been unsophisticated containers for regular batteries, usually of AA type. For builders who used a lot of electrified functions it meant firstly buying a set of rechargeable batteries (for economic reasons and for generally better performance), and secondly removing the entire box from the construction whenever a recharging was needed. Now, with the 8878 box, we witness a new and fresh approach.

The 8878 box will please both PF users and Trains builders. Both groups will benefit from its small size and weight, and the latter one should find the integrated speed dial rather useful. From my personal point of view the new box is interesting for its size and weight alone. Since my main activity covers mobile models of vehicles, the PF battery box was the only large and heavy element whose presence was inevitable in every model. Its size often limited the functionality of a model, and its weight degraded its performance. The 8878 finally enables me to have basically similiar performance while using much less internal space and reducing weight by approx. 160 grams.

The 8878 box comes in a thick foil film, and – somewhat surprisingly – already fully charged. The attached documents contain some pretty obvious notes about not putting it into fire and not throwing away along with the regular garbage, but they also state that it should be charged with the 8887 transformer only. There are two semi-transparent stickers on the sides of the box – one of these summarizes the aforementioned warnings, while the other one includes basic specification of the box. According to it, the box contains a lithium ion polymer battery with 7.4V voltage and 1100 mAh capacity. The dimensions of the box are 4x5x8 studs, and the weight is 75 grams.

Atop the box, there are 4 elements. There is a transformer plug-in socket with a red LED indicator (which flashes during charging and remains constantly alight when the charging is done), a master on/off button with a green LED indicator (remains constantly alight when the box is on), an integrated speed dial and a perfectly usual PF power point. The dial offers 7 forward and 7 reverse speeds just like the 8879  Speed Control Remote does, but here it has fixed neutral and extreme positions, plus a small position indicator. An axle can be put inside it a single stud deep, just like with PF XL and Medium motors. The dial does not return to a neutral position, and operates regardless of the master button – which means that the box can be turned on or off at any dial’s position. This is a pretty comfortable solution if someone doesn’t really need the integrated speed dial (which will be probably the case of almost all mobile remote-controlled PF-powered constructions).

The box has obviously no pin holes, and is only compatible with studs. The speed dial is located perfectly in its center, which should prove comfortable. I was somewhat unsure about the master on/off button, which will be difficult to operate via some mechanism (which was easy with the 8881 box thanks to it’s switch with a pin hole), but I guess that the top of the box will in most cases require a manual access just to handle the recharging, so the box can be turned on or off manually with only little effort.

As for the pros and cons of the box, I’ve made two comparisons in the video. First is a comparison with a set of six AA GP 2500 rechargeable batteries, which I’ve been using as the main power source so far. The 8878 box offers 7.4V voltage (versus GPs’ 7.2 V), 1100 mAh capacity (versus GPs’ 2450 mAh) and 4 hours of full charging time (versus GPs’ 16 hours, which can be greatly reduced with a proper charger). We can easily see that the box sacrifices capacity for the sake of voltage and charging time. Since there is no need to take the box out to recharge it anymore, I consider it profitable – the need to take the entire box out of a model has been most bothersome.

The second is a comparison with the previous 8881 PF box, that is a simple container for six AA batteries. Here the 8878 box offers 4x5x8 studs size (versus 8881’s 4x8x11 studs) and 75 grams weight (versus 8881’s 235 grams). It should be noted that the weight of the 8881 box is greatly determined by the batteries used, and perhaps with another make of batteries this difference would be smaller.

As for the 8887 transformer, it comes in a cardboard box and has a fairly long (over 1.2 m) wire. The one I got was fitted with the UK type plug and marked ver. 3 – I believe there are versions for other plug standards too (e.g. there certainly is an USA version).  It looks pretty ordinary and there are only two places where the Lego name appears.

I believe the new box has an enormous potential, in particular for the model builders. In some cases it should make it possible to build models which were too small for the 8881 box. It has, however, one important downside – the price. Not only is it expensive, but it also requires another product to function properly – the transformer, which is being sold separately and for a considerable price too. Hence I believe that the box will be popular mainly with builders who find the 8881 box way too large and too heavy, and with the ones who have been just about to buy a set of rechargeable batteries for regular use, and who now face an interesting alternative.


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  1. Sariel
    March 2nd, 2013 at 00:23 | #1

    It’s normal.

  2. March 2nd, 2013 at 00:11 | #2

    Hi. My lipo was mostly drained but it only took 2 hours to charge… is this bad?

  3. Sariel
    February 3rd, 2013 at 14:18 | #3

    Sorry, I have no idea.

  4. Maciej
    February 3rd, 2013 at 10:46 | #4

    I have question. I bought for my son such battery 8878 but unfortnunatly my son during one charger took wrong transformer and damaged battery ( battery does not work, leds charger and power no lighting). Question is possible repair such battery? is inside any fuse for protection battery from totaly damage? Is any possibility repair damaged baterry after use wrong voltage by wrong transformer? Thank you for help in advance.

  5. the night yonder
    May 21st, 2012 at 00:31 | #5

    Dosen’t the RPM of a PF XL or M-Motor run slower, because of the current is at 7.4v instead of the regular 9v of the battery box?

  6. Sariel
    May 2nd, 2012 at 16:25 | #6

    Thanks. I’m still using the first one, zero problems with it.

  7. Björn
    May 2nd, 2012 at 16:16 | #7

    Hi Paul,
    3 years after you’ve published this article, how many times did you buy a new battery now, or are you still using the first one?
    I finally bought one (with that overpriced transformer) so I can now start making smaller models too with better response probably, because Li-Po cells also tend to have better characteristics when under load (better than NiCad/NiMH cells that is).
    BTW looking forward to finally see a glimps of your book. As soon as it hits the market, I’ll buy a copy.

  8. Sariel
    March 18th, 2012 at 17:14 | #8

    The switch is plastic. As for the train power regulator – like I said, it should be possible.

  9. March 17th, 2012 at 20:35 | #9

    I have done a little research. It seems like the speed regulator supply is 700 mA, 7VA, 10V AC, the 8887 charger is 10V DC(Sariel, insert more info here, please! :D).

  10. March 17th, 2012 at 19:06 | #10

    About the sounds. I had little time writing my last comment, sorry 😛 Is the main switch made out of plastic or rubber? 😀 Thanks for the quick answer, by the way 😀 You rock!

  11. Sariel
    March 17th, 2012 at 14:50 | #11

    I don’t know, but it should be possible. No, the switch makes no sounds.

  12. March 17th, 2012 at 14:36 | #12

    Umm… Is it possible to use the power supply from the 4548 (train) speed regulator? You know, this: http://ebid.s3.amazonaws.com/upload_big/1/9/5/1322917985-327-37.jpg
    Also, does the power switch make a clickety-clack sound and feeling when pressed? 😀

  13. Sariel
    November 16th, 2011 at 11:12 | #13

    If you use rechargeable AA batteries, then it’s 7.2V as their voltage is lower. If you use regular AA batteries, then you start at 9V and go down from there as they’re running dry.

  14. Maarten
    November 16th, 2011 at 11:05 | #14

    Very useful and clear review, Thanks!

    I was also considering to buy this Li-On power source purely for the reduced weight.

    I was only doubtfull because I was assuming the 8881 suply was 9V versus 7,4 V if the LiOn box.

    But in your review I saw that the 8881 is delivering 7,2 V

  15. Sariel
    September 27th, 2011 at 22:12 | #15

    I was told by people who are into electronics that you can damage the battery with a regular transformer because it has two power cells, not one.

  16. PerryMakes
    September 27th, 2011 at 21:52 | #16

    Regarding the charger (transformer) for 8878 Rechargeable Battery Box – it’s absolutely ridiculous for LEGO to charge what the are for this, and it’s simply not true that you must exclusively use 8887 Transformer to charge the battery. I imagine this claim is made to reduce the chance of people damaging their battery.

    With that in mind – you obviously need the jack to match, INCLUDING POLARITY! (not quite sure of the jack name/size or even if these are standardized. Paul?). Finally, you want the output specs to closely match those of 8887: 10V / 700mA / 7 W. See the ‘Reuse’ section here: http://en.wikipedia.org/wiki/AC_adapter.

    By the way, I did not mind paying for the battery itself. This, contrastingly, is not a common device and offers several major improvements over the alternatives as is pointed out in this blog entry. Thanks Paul!

  17. Mecho12345
    August 30th, 2011 at 08:36 | #17

    Ok thanks

  18. Sariel
    August 29th, 2011 at 23:10 | #18

    Mine is 98 grams, but keep in mind that there can be differences for transformers with different plugs (mine has UK plug). Thanks, I thought it was a time to get some simple logo, at least for the website.

  19. MeCho123451
    August 29th, 2011 at 23:06 | #19

    can you tell me how heavy the charger is? (i am buying one on bricklink) also nice new logo, what bought the change?

  20. Sariel
    February 24th, 2010 at 20:33 | #20

    Sorry, no idea. I’m not even sure it is safe to use a different transformer.

  21. Alex
    February 24th, 2010 at 20:10 | #21


    Hi! Please would you be avle to advise where to buy a cheaper compatible transformer? I have tried my Nokia phone one, but it has a different plug. Thanks 🙂

  22. sqiddster
    December 10th, 2009 at 09:01 | #22

    Hey, just purchased the box – and in response, yes, it does work (yay) with any cheaper transformer, as long as the plug fits the socket. It works even with a lower voltage.

  23. darzeecompany
    July 8th, 2009 at 06:25 | #23

    Awesome! Thanks very much.

  24. Sariel
    July 8th, 2009 at 06:17 | #24

    Yes, of course, it can function normally all the time while being charged.

  25. darzeecompany
    July 8th, 2009 at 05:38 | #25

    Very informative, thanks. I have a quick question for you. Can the battery be turned on while it’s being recharged? I have a simple (stationary) robot project in mind that I’d like to run for days on end, and I’m trying to determine if this will suit my needs before I drop the $75.

  26. Sariel
    June 30th, 2009 at 00:15 | #26

    Yes, they come separately. I have no idea whether the transformer can be replaced by a cheaper one or not. I agree it’s expensive.
    It works exactly like you said – I set it to maximum speed in whatever direction (doesn’t really matter) and then I’m using a handset for control. I have tested it with the new speed control-enabled handset, and it works perfectly.

  27. June 29th, 2009 at 21:00 | #27

    Great review Paul. I have 2 quistion I hope you could answer

    Did you have to buy the battery charger speratly or did it come with the battery? I’ve had a look at the Lego site and it doesn’t look like they come together. It seems very expensive to buy the 2 items seperatly.

    With the built in speed controller on the battery, how do you set it when you use it with the remote control units? Do you set it to maximum speed in one direction?

  28. legobuilder
    June 27th, 2009 at 10:08 | #28

    it’s very compact and useful I like it

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