It's bigger on the inside?

No, it's not the Tardis....

I found this (and another one like it) at school the other day, they have been in a staffroom cupboard since I joined. I think they were for a Roamer, a seventies-looking floor robot meant to teach children about control - they were over a foot wide and not intuitive at all. However, I could never get the damn things to work, so we modernised to child-friendly BeeBots (a lot cheaper and much more fun/accessible).

There must have been some sort of perception filter around these batteries, as it only dawned on me the other day that they are no longer needed. On closer inspection, the Jul-2005 expiry date on them should have been enough for someone to get rid! So I brought them home to dispose at the local supermarket's battery box (if it's big enough!).

These type of batteries have always fascinated me.... I am not the most clued up when it comes to electricity, but do these carry one hell of a charge, or do they last for ages? I can't think why else they are so big! They weigh a ton, so that Roamer must have needed a lot of power in order to move around with one of these inside it. Seems a bit Catch-22ish to me.