Can 2 2s batterys be charged in series?
 

My buddy has 2 - 2s 5000mah lipos. Can he connect them in series to charge them both?

Follow up... Would he charge them at 5amps?

You can,but if you haven't kept them balanced to each other from the start it could get risky.If they don't have the same voltage before they start 1 will get overcharged.But if you start with 2 charged packs then run them in series you should be able to charge in series.It would then be a 4s 5000mah pack.So it would charge at 5 amp

This should help with wiring. http://www.scriptasylum.com/rc_speed/_lipo.html
I would only do it though if the packs are fairly close in age and use, and if they're being run together. Don't do it if there being used separately in a 2s vehicle, then connected together to charge, they will be too far out of balance.