I use one of these:
http://www.ebay.com/itm/320749631694?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITYou can charge at 200/500/700/1000mA, charge AA and AAA batteries, and it's got modes that will charge, discharge/recharge and perform a full refresh of batteries (which appears to discharge and recharge until the total charge they take remains about the same). It discharges at half the charge rate, so if you're running 2500mAh batteries and run a full refresh expect it to take 2-3 days to finish.
It's got four ports and you can use any, all or none of them. If you're putting a lot of current into batteries the recommendation is to charge two rather than four, and put them at the ends to let more air circulate around them.
The link I provided is for the US eBay site, I think you can get them this side of the water but the price will probably reflect the usual 1:1 rate between $ and £ that's so irritating.