Charging Lithium Batteries with a Lead Acid Charger

There is the potential to use chargers that only have Lead Acid profiles, but there are some compromises. Please see below for an explanation of the differences between a Lead Acid profiled charger vs a charger that has a Lithium specific profile, and what the implications are:

1. A Lithium charge profile vs a Lead Acid profile usually has a slightly higher charge voltage and a "deeper" constant voltage phase at the end of the charge cycle, which is able to get the Lithium batteries to a full 100% State of Charge. A Lead Acid profile will not normally be able to achieve this, however it will still get close, say maybe 95% +.
2. The charge profiles have different "return to boost" behavior. After the charger completes its full charge cycle (i.e. it reaches the end of the absorption phase and changes over to the float stage), the charger will then start to monitor the battery voltage, to decide when to switch back to the boost/bulk charge mode and restart a full charge cycle again. The issue is that the Lead Acid chargers will wait for the voltage to drop too low before it restarts the charge cycle - that is because a Lead Acid battery has a lower resting and discharge voltage than a Lithium battery. The implications are that the Lithium batteries' State of Charge may already be quite low by the time the Lead Acid charger switches back into a proper full charge cycle again. On the contrary, a Lithium profiled charger will start to recharge the Lithium battery much sooner. The Lead Acid charger will eventually switch back into a full charge cycle again, but your battery may not have charged much at the end of a drive when you would be expecting it to be fully charged.
   
   There is a potential work-around for this issue which is to shut off the chargers (either via switching the charger off or via a kill-switch installed on the positive line between the charger and the battery), allowing you to temporarily disconnect the charger from the battery. Disconnecting the charger and then reconnecting, should reset most chargers and force a full charge cycle again. This can be useful to do for example just before you leave for a long drive if your Lithium battery has been discharged a fair bit but the voltage may still sit above 13V.
3. Lead Acid chargers tend to have a float charge that keeps putting a trickle current through the battery continuously. This  trickle current is detrimental to the cycle life of a Lithium battery over a long period of time if the Lithium battery is not being used / discharged (it affects the electrolyte). Contrary to this, a Lithium profiled controller will either go on standby after a full charge, or maintain the voltage but with virtually no current flowing which avoids the issue. Please also note that Lithium batteries do not need to be kept topped up constantly (like Lead Acid batteries), because they do not suffer from sulphation if they are stored without being constantly topped up.
   
   Similar to point 2, a work-around is to switch off / disconnect the charger from the battery when it is not being used, to avoid long term float charging.

Alternatively, if this is too much of a hassle or you don’t want the compromises, you can change the charger over to one with a specific Lithium profile.