Today I ran a quick test to see if I could charge my Bluetti Elite 300 power station faster using a fully charged WattCycle 12-volt 300 amp-hour battery. Direct 12 volts into the DC input only gives a slow charge, so I disconnected the Charger 2 from the boat starter and alternator and hooked the battery to those same leads in the engine room with a breaker for safety. The Bluetti Charger 2 steps the 12 volts up to about 56 volts, and the app lets me set the charge rate. Silent mode sat around 250 watts. Turning that off and bumping the limit to 400 watts worked well. At 56 volts, I could push it to 600 watts, and even briefly to over 700, but the long cables dropped the voltage and pulled 60 amps, which I would not want to run for long.
Four hundred watts at 56 volts kept the voltage up and the current more reasonable, so I left it there. The Elite 300 went from about 54 percent to full in roughly four hours. I tried the same idea with another similar battery, and it worked the same way until the source battery got down to around 20 percent. At that point, the voltage sagged enough that the charger just stopped. Shorter cables might have squeezed a bit more out of it, but as a proof of concept, it worked fine. Hope that helps if you have been wondering about using an extra 12-volt battery this way.
Charger 2 with Lithium Battery Source Test Video
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