How shall I charge my Auxilliary Battery?

How many amps was the charger putting out? I'm guessing it wasn't much, but then the Prius doesn't need a lot. Four should charge it up, but don't expect to operate anything for a while. Even a trickle charger will eventually get it done.

However, if the battery was as dead as it sounds like yours was, a smart charger would have assumed it was a 6V battery or might have just refused to charge it.

This is true. But patience is required with a dead 12V. Hooking up a charger doesn't immediately give the battery full power. It takes a while to get it strong enough to run anything and many hours to get it to a full charge.

Nope. Not enough amp hours. I've heard of people using 12V batteries from computer UPSes to run the car, but not to charge a dead 12V.

Sure can. Page 380 in the 2007 owner's manual. Probably about the same page in yours. But the above would still apply.

 

are you sure it's a 2016, or is that just a typo?

if it is the original battery, i would replace it now.

if the car is off, connecting the charger to the under hood jump point is the same as directly to the battery, plus a few feet of heavy gauge wire. you're not running the car.
but you have to make sure you have a good ground.

 

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Haven’t read the whole thread, but:

hooking up either at the under hood jump point, or direct at the battery, should make no difference. I’d suspect your battery is near-knackered, and first time around your (unidentified) charger balked at charging it, but you got lucky with the direct to battery attempt.

per @bisco, how old is it? Also, what’s the charger?

If it’s 4+ years, I’d just replace. If younger, and you want to check it’s condition, electronic load testers are available for DIY, or automotive retailers selling batteries will usually do such test for free. Solar BA9 is a good choice with those, for DIY.

Toyota recommends a charge rate around 3~5 amp, depending on gen. I’d stick with under 5 amp. I’m using a CTEK 4.3, good brand but getting pricey now.

 

Every car owner should have one of the jump packs @bisco linked in post #5, or any of the other brands. I and many others like the Noco ones. I've had mine for several years. About a year ago I charged it back up when it got down to 76%. Prior to that, I'd started a RAM 2500 pickup and two other cars. Haven't needed it for myself yet. I checked it the other day and it's still at 100% charge. It doesn't charge your battery, so you'll still want a charger. But then a battery charger won't get your car going on a dark rainy night at the Dollar General store five mines out of town.

 

One of the experts here may step up to correct me but here’s what I concluded after being in a similar situation with a dead battery…

The brake booster gets in the way of making progress with a small charger unless the 12v battery is disconnected. Once the driver door is opened the brake booster is activated and neither the dead battery or a small charger will ever supply enough power to bring the pressure up and shut it off. You’ll observe the charger cycling and hear some brake booster clicking but there’s never enough current to spin the pump. The booster presents an ongoing load which prevents the battery from ever charging. This explains the repeating pattern that the OP was seeing.

Perhaps an old school charger with sufficient amperage would get around this quirk or even “jump start” the car but I didn’t sort this out. I crawled into the hatch area…

 

I think you pretty much nailed it. At least that's my exact experience with the Gen 2 models. Sometimes my cars sit unused for a month or 2 or 3. I always charge from under the hood using a 1.5amp charger.

 

That's about right, with a small naming quibble: it's the "booster pump" that presents that load. (All Prius generations have a "booster pump". Gen 1, Gen 3, and Gen 4 also have a "booster", while Gen 2 does not. And in all the gens that have both, they're in two different assemblies, so talking about the "booster" or the "booster pump" means talking about different things. So it gets confusing.)

So if you need to jump a Prius, it is good to know how to stop the booster pump from running while you do that. In Gen 2, you can either pull out both the ABS-1 (25 amp) and ABS-2 (30 amp) fuses, or pull out the ABS MTR and ABS MTR 2 relays.

Then jump the car. You'll probably have some brake trouble codes because of the pump not running, but you'd rather have a started car with some brake trouble codes than a car you can't start. Once it's READY, put the relays or fuses back in. The pressure should then pump up and the beeping stop. The warning lights should go out on their own within a few drives, or can be cleared if they don't.

 

The booster pump (or booster) runs for 10~15 seconds tops. How about connect jumper cables, and just wait a few minutes (pump runs and has long stopped) before trying to start. IIRC this waiting period is a good idea with any car?

 

Yeah, the brake brake booster thing is news to me, and very interesting