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I was reading John Blackburn’s comments on Li-Po (lithium iron phosphate) batteries in RC155. You should be very clear that this type of battery needs ‘constant current’ charging, which is distinctly different from normal automotive systems and chargers which are of the constant voltage type.

As its name suggests, a charger used to charge Li-Po batteries supplies a constant current while allowing the voltage to ‘float’. This charger monitors the terminal voltage to control the charge rate and to determine what state the battery is in. Trickle chargers, normal lead acid battery chargers and automotive systems are then not suitable to charge this type of battery as they hold the voltage at 13.8 Volts and allow the current to ‘float’. This is not a good situation for a Li-Po battery.

However Li-Po is tolerant to some abuse, as John mentioned a lithium ion battery would fail in spectacular fashion. Better quality brands of Li-Po batteries have a built-in charging regulator inside the battery. The Motobatt lithium range for example have circuitry to protect the battery from ‘overcharging’ by an unqualified charger (this means automotive systems). Motobatt lithium also have another protection feature to protect against over-discharging. Li-Po batteries will shut down completely with no chance of recovery if you over-discharge them. This could happen when trying to start an engine that won’t start or inadvertently leaving the ignition on. Many Li-Po batteries don’t have this level of protection.

There is a range of Li-Po batteries available, you should check what on-board protection they have, also you need a special type of charger – a lead acid battery charger / maintainer is no good for a Li-Po battery. For more information on Motobatt Lithium contact me on 01580 880768. Marcus, rexs-speedshop.com