2016 Prius c 12 V battery dead, how do I recharge it?

You can use the underhood terminals to charge the 12v battery. You should look for a smaller one, or one whose output can be turned down to 2-3 amps.

Harbor Freight sells a decent one for $29. 2A rating and has reverse polarity protection.

 

Battery Tender Jr is about $35 and has an easy to use permanent cable that attaches to your battery and enables quick connects.

Use for storage situations of ten days or longer even though a new battery can last three weeks.

 

I don't consider that charger from Harbor Freight to be "decent".

While Battery Tender is a good brand, 800 MA max. capacity isn't
very versatile; it is made mostly for small batteries like motorcycles and
lawn mowers.

Something with a 2 to 4 amp capacity is a better choice, in my opinion.

IF.......you get a good automatic tender type charger......and the car is near a power
outlet when not being used, then leaving it connected while you are gone would
be a better plan than what you have been doing.

 

Where was the car for these hiatus, at the airport, at home, and if the latter, what's your parking situation?

If at all practical, connect a smart charger, rated around 4 amps or less, before your trips.

I'm using a CTEK 4.3 (believe current itteration is CTEK 5); it's been very dependable. Our usage is very spotty now, as little as one drive per week, albeit decent length, and we try to consolidate shopping/chores with those uses. Yearly usage around 3000 kms.

Our battery's just past 8 years old now, tests like new. It's on the charger 'round the clock, not detrimental: it runs a charging session, then subsides to light "trickle charge".

 

All you have to is supply more than the 30ma the car continuously consumes. Once the car goes to Ready the inverter’s dc to dc does all the 12v heavy lifting up to 100 or more amps.

 

Actually the first step is to measure your battery voltage. If it is very low (say, below 9V), many of the smart charger with limited capacity (a few amperes) may not be able to revive it. You may need a stronger charger to start with, or parallel connect your battery with another fully charged battery, then charge it with a smarter charger.

 

What will it take to get you to STOP using that incorrect terminology ??

It does NOT "trickle charge".

It does drop to the "float" voltage step in the automatic routine or stop charging completely
as it monitors the need for additional charge.....depending on the model of smart charger.

 

When do we get to vote?​

 

Sorry Sam.