Not sure if this thread is still active but thought I'd throw my two penneth worth into the mix. We have 2 Spykees in the house, one belongs to my son and I bought one to play around with too. Both suffered poor battery performance when new so I obtained a 2600mAh from a guy regularly advertising on Ebay (cellpack solutions). The Spykees both now perform adequately. I'm currently working on the Arduino head tilt mod for my Spykee and looking to modify the base to put a reed switch magnet. (This is a requirement with the Arduino mod) and am interested in getting around the recharge issue with the new bases supplied by Meccano. To be quite frank, I'm not impressed at all with the way this new base has been rolled out without thinking through the consequences. If the charging circuit was designed properly in the first place, it would use "Delta peak cutoff" to prevent overcharging and these controller chips are widely available, resulting in rapid charge switchover to trickle once pack is fully charged. This means Spykee is ready to go at any time. I've never experienced the overheating issue and am considering junking the new base and returning to the original. As a safety feature, I might mount a thermistor in the base beneath where the battery pack sits and use this to cut off the charge if it overheats. Any suggestions please feel free to reply and it's good to see that others out there are experiencing the same problems. Maybe Meccano, if your reading this, can suggest a fix.