I need to make as close to 48-52v as my current works as possible so I have been looking at 7S lipos now to make either 5ah or 10ah or 20ah pack (totally other combination would be needed for 15ah). I only have two choices.  The 5800 is out of stock where as this 5AH pack is in stock for $60 each.

 Capacity: 5000mAh
Voltage: 7S1P / 7 Cell / 25.9V
Discharge: 25C Constant / 35C Burst
Balance Plug: JST-XH
Discharge Plug: 5.5mm Bullet

Weight(g)	818
Max Charge Rate (C)	5
Length-A(mm)	158
Height-B(mm)	46
Width-C(mm)	53

There are no 7s chargers I know of but an 1-8s charger should be able to do it.  This one is $40.

Capable of charging any size Lipoly battery up to 8 cells or at 7A.The ECO-EIGHT includes Auto current detect and temp, amp, voltage safety features to prevent over-charging. The ECO-EIGHT includes an array of charging plugs and wires to suit almost any application and comes with JST-XH balancing plugs so you can charge and balance your ZIPPY/TURNIGY packs easily.Input power is 11-18v, perfect for car batteries or a pc/laptop powersupply.
Features;Microprocessor controlledHigh power and High performance circuit with maximum power of 150WDelta-peak sensitivity (NiMH/NiCd)Individual cell balancingLi-ion, LiPo and LiFe capableNi-Cd and NiMH capableLarge range of charge currentsFast & Store function, allows safe storage currentTime limit functionInput voltage monitoring. (Protects car batteries at the field)Data storage (Store up to 10 packs in memory)

Spec.Input Voltage: 11~18vCircuit power: Max Charge: 150W / Max Discharge: 5WCharge Current Range: .1~7.0ANi-MH/NiCd cells: 1~27Li-ion/Poly cells: 1~8Pb battery voltage: 2~36vWeight: 574gDimensions: 170x110x35mm

I'm not sure but it would seem it will take a long time charge and I would need four chargers, so if I rode to somewhere to charge up I'd have to carry more than 2kg in chargers and wait much longer?

http://www.hobbyking.com/hobbyking/store/__12104__HobbyKing_ECO8_150W_7A_8S_Bal_Dis_Cyc_Charger_w_acc_.html

http://www.hobbyking.com/hobbyking/store/catalog/21374.jpg



http://www.hobbyking.com/hobbyking/store/__21374__ZIPPY_Compact_5000mAh_7S_25C_Lipo_Pack.html