# Battery Sizing

Registered Users, Users Awaiting Email Confirmation Posts: 1
Hello Is there any easy formula to calculate no of battery if there is given watthour, known system voltage.
like as Required Battery capacity= 7200 WHr And system Voltage is 48v
It comes 150 Ah .
Do u have any idea plz
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• Solar Expert Posts: 9,583 ✭✭✭✭✭
If your design comes up with 7200 wh being required  (Is that the daily load, or the final 20% discharge value)
7200 / 48v = 150 ah indeed.   Easy way is to use 8, 6V 200ah golf cart batteries in series.  Gives you a little extra
capacity, no parallel strings, and should be a solid 3-6 years lifetime.
Your charging source should be able to provide 20A @ 58V or about 1200W from a wall outlet, or about 1500w of well aimed PV panels.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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• Registered Users Posts: 395 ✭✭✭
Hello Is there any easy formula to calculate no of battery if there is given watthour, known system voltage.
like as Required Battery capacity= 7200 WHr And system Voltage is 48v
It comes 150 Ah .
Do u have any idea plz
Yes, your formula is correct but ...
I would double the size of the batteries.
If you calculate 150 AH needed per day, then install 300 AH batteries  for 50% DOD max.
8 batteries x 300 AH x 6 volts each in series.
3 years at 50% Depth of Discharge = 1,000 deep cycles.

There are not very many batteries that can handle 50% DOD every day for 3 years.
Don't even think about using Marine (fake) "Deep-Cycle" batteries.