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

Lipo from hobby king

From Hobby king trying to get the right combinations is really annoying.  It important to remember when working on batteries combinations:

in Series you are doubling the voltage while keeping the same (amp hours), and in Parallel you are doubling the capacity (amp hours) while keeping the same voltage.

I want the most amp hours so an 8AH would be best as that is the highest amount which seems to be easier to get to the voltage requirements.

http://hobbyking.com.au/hobbyking/store/__20647__zippy_flightmax_8000mah_6s1p_30c_usa_warehouse_.html
http://hobbyking.com.au/hobbyking/store/__19531__zippy_flightmax_8000mah_6s1p_30c_aus_warehouse_.html
I'd only need two of these but always out of stock.

http://hobbyking.com.au/hobbyking/store/__23684__zippy_flightmax_8400mah_3s2p_30c_lifepo4_pack_usa_warehouse_.html I would need 5 of these to get 50v @ 8AH 4kg battery for $325 for LIFEPO4
Capacity: 8400mAh
Voltage: 3S2P / 9.9v
Discharge: 30C Constant / 40C Burst
Weight: 772g (including wire, plug & case)
Dimensions: 147mm x 52mm x 53mm

I could have 3 to get a 55v for a 5 ah at 2kg or 6 to get to a 10 @ 4kg 

 pack http://hobbyking.com.au/hobbyking/store/__8581__ZIPPY_Flightmax_5000mAh_5S1P_20C.html

Capacity: 5000mAh

Voltage: 5S1P / 5 Cell / 18.5v
Discharge: 20C Constant / 30C Burst
Weight: 640g (including wire, plug & shrink wrap)
Dimensions: 147x52x43mm

Would I need two 8s chargers? Controller experts help please. I want to change my battery but am scared I might fry the controller. It's a "Crystalyte 36V-48V 40A digital controller 
12 Fet (4110)" and the current battery is 48v10Ah LiFePO4 Headway 38120S cells BMS Rated at 40A Continuous, 60A Peak. The 5A charger output 58.4VDC. Fresh off the charge it rests at 58v and slowly goes down to around 52v underload between 50-47v etc as she goes down... I want to get two of these in Paralel so 29.6 x 2 = 59.2v 
http://www.hobbyking.com/hobbyking/store/__19158__Turnigy_nano_tech_5000mah_8S_65_130C_Lipo_Pack.htmlwill the controller handle it? I really don't want to buy another controller. And I really don't want to go to a 44v combination of lipo. http://www.hobbyking.com/hobbyking/store/__12104__HobbyKing_ECO8_150W_7A_8S_Bal_Dis_Cyc_Charger_w_acc_.html
other option:
http://www.hobbyking.com/hobbyking/store/__9005__iCharger_208B_350W_8s_Balance_Charger.html

cheaper charger 

http://www.hobbyking.com/hobbyking/store/__6443__G_T_Power_A8_8Cell_balancer_Charger.html

dual charger - so don't need to buy 2.will add more soon