A battery turns stored chemical energy into electrical energy. Each cell gives a fixed voltage set by its chemistry, not by its size; a battery is cells joined in series for voltage and in parallel for capacity. Batteries run handhelds, make portable and emergency stations possible, and back up the shack's power.
Chemistries
Chemistry
Nominal cell voltage
Recharge?
Notes
Alkaline, carbon-zinc
1.5 V
no
single use
Lead-acid (flooded, AGM, gel)
2.0 V
yes
cheap and heavy; 6 cells make "12 V"
NiMH (and older NiCd)
1.2 V
yes
the common rechargeable AA and AAA
Lithium-ion
about 3.6 to 3.7 V
yes
high energy for the weight; needs a protection circuit
LiFePO4 (lithium iron phosphate)
3.2 V
yes
lighter than lead-acid, tolerant of many cycles, more forgiving of abuse than other lithium types
Nominal voltage is a mid-discharge average. A fresh battery reads higher and an almost-empty one lower, and every chemistry has a minimum below which discharging does harm. For a 12 V lead-acid battery that is about 10.5 V; for lithium types the protection circuit enforces it.
Series adds voltage; parallel adds capacity. Nominal values: real voltage rises when charged and sags when discharged.
Pack12.8 V · 10 Ah
What the numbers mean
A real battery behaves like an ideal source in series with a small resistance. Pull a large current, such as a transmitter keying up, and the terminal voltage sags. Lower internal resistance means less sag and more current available.
Terminal voltage = 12 V minus (current × internal resistance). Low resistance means little sag.
Same load, same current30A
Capacity tells you runtime: hours = amp-hours ÷ average current. A 10 Ah battery supplying a 2 A load lasts about 5 hours, less if you must stop before it is flat or the battery is cold or old.
Hours = amp-hours ÷ amps. More current drains it faster.
Operating time12h
Charging and safety
Use the charger made for the chemistry. Lead-acid, NiMH and lithium cells each need a different charging profile; the wrong one overheats or ruins the cells.
Never short a battery. A big battery can deliver hundreds of amps into a dropped wrench or bare cable, melting metal and starting fires. Fuse the lead close to the battery.
Lithium cells can burn. Do not puncture, crush or overcharge them, and stop using one that swells, hisses or gets hot.
Charging lead-acid releases hydrogen, which is explosive. Charge in a ventilated space and keep sparks away.
Batteries hold a lot of energy. Short circuits and rapid charge or discharge turn it into heat and gas.
If you swap a battery into a radio that expects 13.8 V, check the radio's allowed supply range against the battery's full and empty voltage.