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I have an inverter that currently uses a single 7 Ah lead acid battery.

While the rating of the inverter is sufficient to my purpose, the battery does not provide nearly enough run time, and being lead acid, does not do well at charging and discharging all the time.

I want to replace the battery with a 100 Ah LiPo.

This presents 2 problems:

The built in charger of the inverter is built for lead acid and not LiPo.

And even if it was, it would take years to actually fully charge a 100 Ah battery.

Can you, through the use of a diode, isolator, etc "block" the inverter from trying to charge the battery while using an external charger to make sure that the battery is charged?

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  • \$\begingroup\$ Please draw a block diagram. With some luck, you could just hook up an external charger to your battery and not separate anything, but the devil’s in the details and you have provided very little of them. What’s the open circuit voltage of the built-in charger? \$\endgroup\$
    – winny
    Commented Feb 11 at 16:16

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Yes, it can be done, but not with a simple diode isolator circuit. You would need two power MOSFET circuits rated for at least 20 A, one between the battery and the inverter, and one between the battery and its external charger. AND, monitor and control circuits to run everything.

Basically, a large electronic SPDT switch.

NOTE: This is not a beginner project. Better to buy a medium-sized, mechanical SPDT switch: a 30 A automotive relay on ebay for $5. Controlling that is both easier and safer.

NOTE: If you are thinking of building your own LiPo charger, please don't. Sony learned that there are over 2 billion reasons to be very careful with 5 A-h batteries, let alone 100 A-h.

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i want to replace the battery with a 100AH LiPo

That means you need a different UPS / "inverter" (it's not actually just an inverter); full stop. Practically nothing of what you currently use is useful. Your diode logic will not work; any reasonable lead battery controller would detect the different voltage of a Lithium battery pack as fault and refuse to work, to avoid catastrophic failure.

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