Damn...again!

I fixed the broken bit on Kaizer (one of the lifting fork mounting points) Its now been reinforced to make it stronger and Im much happier with it than I was before it broke.

Running it around the kitchen let me get a feel for it although I wont be driving it much at Rebel Robots. Its nippy (so Im feeling more confident about keeping away from the discs of Kishar and Hornet 2) and quite controllable, nice to drive really. As a last test before stopping for the night, I spun it on the spot continuously while raising the lifting forks. I could hear the batteries running down a bit, which is what I wanted so I could trickle charge them again, when all of a sudden....POP!

One of the cells in the pack exploded (not violently, just the loud pop) and damaged another cell in the process. This has left me in a bit of a sticky situation. Im going to go on the hunt for a powerful soldering iron and attempt to make a pack up from the surviving working cells of this pack and the spares from the pack Drumroll damaged. But in the event that Im not able to, or the homemade pack assembly doesnt go too well, can I ask...

Does anyone have a spare pack (either new or used) of 9.6V 3700mAh Nimh batteries in a 4x2 block formation eg:
http://cgi.ebay.co.uk/9-6v-3700mAh-NiMH-Battery-Pack-Compact-Vapextech_W0QQitemZ320160397744QQcmdZViewItemQQptZ UK_ToysGames_RadioControlled_JN?hash=item320160397 744&_trksid=p3286.c0.m14&_trkparms=72%3A1683%7C66% 3A2%7C65%3A12%7C39%3A1%7C240%3A1318http://cgi.ebay.co.uk/9-6v-3700mAh-N...tech_W0QQitemZ 320160397744QQcmdZViewItemQQptZUK_ToysGames_RadioC ontrolled_JN?hash=item32016039 7744&_trksid=p3286.c0.m14&_trkparms=72%3A1683%7C66 %3A2%7C65%3A12%7C39%3A1%7C240% 3A1318

that they could bring to Rebel Robots at the weekend as a standby. A new pack off eBay wouldnt arrive in time but if I was to borrow someones pack Id be willing to buy it off them after the event if they wanted to part with it. If anyone can help out, Id be most grateful!

Additionally, does anyone have an idea of what would cause a cell to pop like I described? Is it due to drawing too much current out of the battery, more than it can handle? Im guessing this is the main reason since Kaizer was spinning on the spot and running the actuator at the same time. My other concern is, spinning and lifting the forks is a likely arena scenario, so its not ideal to have cells popping during a fight. Is it possible that the application would be more suited to Nicads (or possibly A123s now that Nicads are hard to get) since it seems to be drawing a lot of current. The setup is four 16.8V drill motors running at 19.2V, plus an Okin Deltadrive actuator driving the forks.

Any insight into the above in relation to battery technology would be helpful, as Im still quite uneducated in that department (too used to the simplicity of SLAs )

Thanks