For the past decade anna arf I've owned one of these...
http://tinyurl.com/gbh12vre
Which is a great old drill, but in recent years replacement batteries
have been a problem - in that, while they were current, the prices being
asked were ridiculous and I was reluctant to pay that. A couple of
strategies were employed; using an old battery as a terminal for a
flying lead set to a start'ncharge set, and re-celling another battery,
with moderately successful results, but the Bosch charger isn't kind to
batteries. Now, the replacement batteries for this model seem to have
dropped off the radar entirely.

Anyway, today I decided to try sticking a Makita 7.2V battery in the
Bosch - stone me, it worked fine. Slower, obviously, but it turned in a
lively fashion. Turns out the battery keyways, which are supposed to
prevent wrong insertion, don't prevent an old-model Makita battery from
going into a Bosch of this vintage.

This opens a new door, for last night I found this, a Makita 12V
extended battery that is the same shape as the 7.2V one, and has a few
extra cells down the bottom, where they won't be in the way, and it's
cheap; 9 quid. This is a 1500mAh, slightly better than the original of
1.3Ah
http://www.a1-battery.co.uk/POWER_TO...TA/TMK034.htm#

Even better, there's a 3000mAh NiMH one for 35 quid
http://www.a1-battery.co.uk/POWER_TO...ITA/TMK045.htm

I already have the Makita charger for these, so that's no problem.