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Cycle Life
Batteries are rated to show how many charge/discharge cycles they are able to
endure before their health falls to a point where replacement is necessary. This
is typically expressed as XX # of cycles to XX% discharge. It means that if you
discharge to a lower value each time before re-charging, the total times this is
done is lower than if the battery is only discharged a smaller amount each time.
Of course, this is in a laboratory setting, as nobody discharges their batteries to
a set point each time before re-charging, and many other factors will contribute
to how long a battery lasts. For lead acid batteries, these also include:
1. Ambient temperature.
2. If the battery is fully charged after discharge and how much time passes
between the two steps.
3. If the battery is actually fully charged, instead of “Almost fully charged”
4. If the battery is over charged, at voltages higher than the manufacturers
recommendations
These factors together mean that in real-life applications, most batteries never
reach the cycle life proposed by manufacturers.
Partial State of Charge (PSOC) Cycling
All lead-acid batteries benefit from being fully charged back to 100% after
each use. PSOC means discharging a battery to some point, and then not
fully charging back to 100%, before discharging again. For some users, this
is not an issue as their batteries are not often left in a partial state of charge.
Boaters using battery powered trolling motors typically charge their batteries
fully right after use. For others, perhaps boondocking in an RV or cruising (and
anchoring) in a sailboat, this plays an important part in battery usage. Current
wisdom says when 24/7 charging is not available for lead acid batteries
(including AGM) the best balance between cycle life and maximizing capacity
is to discharge the batteries to 50%, and then charge back up to 80%. Then,
perhaps once week, charge up to 100%. As batteries close in on around 80%
charge, the current they accept diminishes. This means that the time it takes
to get the last 20% into a battery can become excessive. This becomes clear
when running an engine or generator to charge batteries.
Summary of Contents for SG200
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