SOME GOOD LINKS:
Car and Deep cycle Battery FAQ]
esp. The
Car and Deep Cycle Battery Frequently Asked Questions (FAQ) 2012
Century Yuasalinks:
Different types of batteries and
Battery charging
DEFINITIONS:
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Cold cranking amperes (CCA) is a measure of RATE- How fast the battery can deliver its energy- that's how much current (read: starting grunt) the battery can supply at -18C (0F) for 30 secs. So a perfect fully charged 450CCA battery should supply 450A at >=12V for 30secs at -18°C/0°F.
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Ampere Hours (Ah) is a measure of the BATTERY electrical charge CAPACITY- How much the battery can actually deliver.That is, the TOTAL electrical charge (effectively energy) the battery can supply. This is measured when discharged at a specific rate at a specific temperature. Generally, this is the maximum current the battery can supply continuously for 10 hours at 20C. For example, if a fully charged battery can maintain a maximum 5A for 10 hrs continuously at 20C, it is rated at 5A x 10hrs = 50Ah. These values are seldom printed on car batteries.
TEMPERATURE
The main environmental effect is temperature. Here’s how things varies with temp:
#1 RULE: HEAT KILLS BATTERIES
Changes with temperature:
- Useful Capacity (Ah) increases with temp
- Useful Discharge Rate (CCA) increases with temp
- Evaporation increases with temp
- Plate sulfation increases with temp
- Plate degradation increases with temp
- Overall battery lifespan decreases with temp
OTHER FACTORS:
- Lead acid batteries are designed to operate at ~20-25C. Seldom is your vehicle’s battery at this temperature!
- Internal damage results from impacts, vibrations, overheating, overcharging, total/deep discharging sulfation, plate erosion. This reduces the battery capacity:
[indent] o Vibrations and impacts damage the plates. Bits break off reducing the plate size and therefore battery capacity. Broken bits can short a cell effectively negating it (removes ~2V, no capacity from that cell)
o Overheating, overcharging can evaporate the water. This concentrates the acid accelerating plate wear and reducing capacity.
o Overcharging can cause overheating, physical damage (warping) and battery explosions.
o Total discharging damages the battery permanently reducing its total capacity. The plates also ‘sulfate’ blocking current charge/discharge as the sulfates are non-conductive.
o Overcharging/discharging can cause excessive heat (accelerated plate wear), plate fracture and plate bending. Any touching and the cell is shorted.[/indent]
- Higher Temperatures accelerates the battery’s chemical reactions. This:
[indent] o Increases the amount of energy you can extract from the battery (effective Ah).
o Increases the rate at which you can extract the energy (effective CCA). This is why batteries tend to fail on cold days (lowers the CCA available)
o Accelerates plate damage. Apparently, you can expect to halve the battery life for every 10C over 20C.
o I.e. live fast, die young![/indent]
- CCA vs Ah: Think of this like a water tank with a pipe outlet:
[indent] o CCA is determined by internal plate area. Higher CCA = more plates in a give size = thinner plates = more fragile = possibly shorter life. It’s like the pipe diameter out of your water tank. Big pipe on small tank = quick empty.
o Ah is determined by the mass of Lead. Bigger battery = more Lead = more chemicals = more energy = more Ah. Like a bigger tank.
o Large CCA and small Ah (small battery size) simply means a small battery that can be drained quickly with possibly fragile plates.
o Smaller CCA = larger plates = probably more durable
o Larger battery = (in general) larger Ah = larger energy storage.[/indent]
OTHER THINGS:
- The lead acid battery is a high purity balanced chemical reaction. Keep it that way by avoiding contaminants and only used distilled/demineralised water to top it up.
- Impure water (such as tap water) can introduce salts that either produce gases (e.g chlorine), or salts that block the reaction and reduce battery capacity and lifespan.
- Batteries can be designed to protect against jarring/vibration, heat and other damaging effects. You just need to buy the right one.
- AGM (Absorbed Glass Mat) help protect against vibration/jarring.
- Deep discharge is anything below 12V, although with a supposedly charged battery the terminal voltage will be <12V if there’s a shorted/dead cell.
- Look at the links above for more info!
Hope this helps,