I just installed lithium batteries on my sailboat and have a lead acid starter battery and separate chargers for starter and house and a DC to DC Charger for the alternator. My battery monitor ( was installed when I had all FLD batteries) shows when the battery switch is on HOUSE OR START it draws .04 amps (due to the compostable head fan) BUT on Combined it draws 8 or 10 amps then down to 2 amps after one minute. is that because the lithium is providing power/charging the starter battery? I have checked everything and can't find the source of the draw.
lithium battery conversion
- Thread starter Andiamo 34
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Hard to say for sure without knowing more about your wiring layout. It certainly sounds possible that you’re reading current flow from house into starter when the switch is set to both. If that’s the case you would probably never really want to keep the switch on both, as paralleling lithium with lead is frowned upon in general.
Thank you and Yes that is the only time they see each other, the DC to DC Charger is isolated as well. It's the only conclusion/ thought that I could come up with since I disconnected everything on the house side and the Battery monitor is only connected to the house neg. Bob
Did you insure the charger you had was compatible for use with a litium battery? I looked into converting to litium for some time and there was so much conflicting information out there about the charging system when converting from lead or AGM to litium I decided to stick with AGM.
Yes I did. I bought Redodo batteries and the Redodo charger and completely separated starter bank from house bank
As David says - you shouldn't parallel Lead Acid and Lithium - the Lead Acid sits at 12.8V roughly, and the Lithium at 11.4 - the Lead Acid will to do an uncontrolled charge of the Li battery - not a good thing! 
This article while long will explain drop-in LFP conversions.
Drop-In LiFePo4 - Be an Educated Consumer
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Drop-In LiFePo4 - Be an Educated Consumer
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The resting voltage of a nominal 12V Lithium iron phosphate (LiFePO4) battery is around 13.2-13.8V. 11.4v is considered discharged. I guess if you hooked up a FLA battery to a discharged LFP battery you would see current flow, but I doubt it would be catastrophic. Anyway that's not the reason they should not be paralleled. The charge requirements are quite different and favoring one is to the detriment of the other. The discharge characteristics are also different.As David says - you shouldn't parallel Lead Acid and Lithium - the Lead Acid sits at 12.8V roughly, and the Lithium at 11.4 - the Lead Acid will to do an uncontrolled charge of the Li battery - not a good thing!