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koates · 08-24-2020, 06:45 PM

Lawson, Your battery tender or charger has an output of maybe up to 10 amps or less depending on which model it is. Check the specifications of the one you have. When your starter motor is cranking your engine it is drawing anything from 150 to 250 amps out of the battery. If your tender is connected to the battery during this cranking cycle then also the starter is trying to draw power through the tender. The starter might be trying to draw say 80 amps through the tender which is way over its current capacity. Components inside the tender such as the rectifier or transformer were not designed to do that and damage may be the result. If your tender is still OK then you have been lucky. You should not do that. Regards, Kevin.

08-24-2020, 06:45 PM	#5
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,079	Re: Battery Tender light vs Ammeter query Lawson, Your battery tender or charger has an output of maybe up to 10 amps or less depending on which model it is. Check the specifications of the one you have. When your starter motor is cranking your engine it is drawing anything from 150 to 250 amps out of the battery. If your tender is connected to the battery during this cranking cycle then also the starter is trying to draw power through the tender. The starter might be trying to draw say 80 amps through the tender which is way over its current capacity. Components inside the tender such as the rectifier or transformer were not designed to do that and damage may be the result. If your tender is still OK then you have been lucky. You should not do that. Regards, Kevin.