Sorry. not true. If the charger has capacitors inside, then the inrush current can cause a spark at the battery terminals irrespective of whether the charger is powered or not.

The Deltran Battery Tender JR that almost everyone I know uses (including myself) is advertised as spark proof. While you're 100% right electrically- I think they've engineered it to do the opposite and even prior to putting voltage through check for both terminal connectivity.

That said- I still connect while unplugged because I'm a giant wuss.

Sure, it depends on the charger design. A good design should not spark.

My comment was aimed at the general statement made about not getting sparks without ‘connecting a power source’.

We have all seen this. Forgetting chargers, pretty much all newer cars will spark just on battery connection. This is caused by the multitude of capacitors charging almost instantaneously in all the electronic devices onboard . This inrush current can be quite high - could be several hundred amps but only for a short period of time.

^^^ Done

Actually there is some remote theoretical risk of detonating hydrogen gas created by electrolysis of water during the charging of a battery when you disconnect your clamps, that's why instructions usually have you unclamp a remotely attached ground connection first.... doubt that a tender could ever create enough hydrogen.

My CTEK has battery clamps and a socket for connection to a dc port. So I just plug it in. It takes a few seconds.