The thicker the plates, the better.  Actually "deep-discharge" is something
of a misnomer - Discharging a cell to say, 20% of capacity is just as
harmful in a "deep-discharge" cell as an "Auto" cell - It just takes longer,
and the deep-dischg cell will tolerate more deep cycles because the plates
are thicker.

Runners-up are "traction batteries", "marine batteries", "golf-cart batteries".

You may not get what you pay for, but you surely won't get what you don't pay
for - As someone mentioned, price is a good index. deep-discharge batteries
are expensive.

A good source for cheap lead-acid cells is medical equipment - Quality stuff,
generally maintained on trickle-charge for their tour (usually two years), and
then replaced. These can be in near-new condition, if you can get them before
they've sat on some surplus dealer's shelf for years...
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist