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LEGO → TECHNIC → Power Functions
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8878 Power Functions Rechargeable Battery Box is a TECHNIC set released in 2009. It needs 8887 Transformer 10VDC (purchased separately) to charge it.


The battery box measures 8 studs long, 4 studs wide and 4 bricks high, exactly the same as 88000 Power Functions AAA Battery Box. It has a Lithium Polymer rechargeable battery pack that can power 2 XL motors or 4 M motors at one time. The box is mostly dark grey with a light grey top. On top is a green on/off button with an LED indicator, an orange 15 position speed dial with an axle sleeve connection, a connection point for power cables and a charging jack. This battery box is occasionly used in Trains sets.

While charging, the LED indicator will be lit. When the battery pack is fully recharged, the LED will blink.

The speed dial has a middle "neutral" position, 7 forward speeds and 7 reverse speeds. It can also be used to precisely control the Servo Motor.

The battery box will automatically turn off after 2 hours. However, if the transformer is connected then the battery box is constant on and you can use it continuously, drawing power from the transformer instead of the battery pack.

Despite the LEGO description saying that their 10V DC charger is needed, any 9-12V charger with a compatible jack can be used without damaging the batteries. Description This is a description taken from Do not modify it. (visit this item's product page)

Charge up your LEGO® Power Functions!

No more disposable batteries! This rechargeable battery box has built-in Lithium polymer batteries for low weight and maximum power. Use it in your LEGO® Power Functions models and never have to use disposable batteries again!

  • Use the #8887 10VDC LEGO Transformer to charge the battery!
  • Motor speed can be controlled via the battery box speed control dial!
  • Output voltage is 7.4 V!

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