| Think of your electrical system using a hydraulic analogy. Consider the battery is a six foot diameter one foot deep wading pool full of water. At the bottom of the pool is an three inch diameter drain pipe capped-off with a valve. Pumped water enters the top through a one inch diameter pipe.
Using this analogy,
Discharge current is the flow rate of water out of the pool
Charging current is the flow rate of water into the pool
Battery capacity is the volume of water in the pool.
Battery voltage is the water pressure at the bottom of the pool
Operating Condition: Storage
The drain valve is shut but the pool leaks a little (current). Every so often you put some more water in (trickle charging) the pool to make-up any water level (voltage). Over time the pool leaks more and more.
Operating Condition: Startup
Water flows (discharge current) rapidly out the open drain until simultaneously its valve is quickly shut and the pumped water (charging current) flows into the pool. During this time the pool has lost a gallon or two of water and the water level (voltage) drops a little.
Operating Condition: Normal Running
Water enters the pool faster than the water flows out the drain. After a while, the pool water level (voltage) rises and eventually overflows (fully charged battery).
OK, so what happens in this analogy if you use a smaller battery?
Instead of a six foot diameter one foot deep wading pool, suppose you have a three foot diameter one foot deep washtub.
Operating Condition: Storage
The washtub leaks at the same rate, so you put in some more water. Since the washtub is smaller the water level (voltage) drops faster so you have to full (trickle charge) it back up more often and for longer periods of time.
Operating Condition: Startup
Again, water flows rapidly out the open drain. But now the water level (voltage) has dropped much lower due to the smaller amount of water held by the washtub. The volume of water lost from the pool and the washtub is about the same.
Operating Condition: Normal Running
Again, water enters faster than the water drains, eventually overflowing the washtub, taking the same amount of time as before.
The principal advantage of using a larger battery is to be able to restart repeatedly. If you regularly don't ride long enough to recharge fully between restarts, stay with a larger capacity battery. Deep discharges will reduce battery life. A lower amp-hour battery will need to be trickle-charged more often.  |