Prius 12V battery charging at 14.9V/10A???

It is ok if the battery was in a significantly discharged state. I think a Battery Tender Jr would be a good $30 investment if that battery is not fully charged yet. You should see 12.7v after running it enough to get a full charge. That standby voltage may drop overnight to maybe 12.4-12.5 on a new battery so you are probably ok. Don't keep the keyfob too close to the car as it will increase standby current and ensure your map lights and cargo light goes off.

 

But only for a short period of time......like maybe 5 minutes or less.
I second the suggestion for leaving it on a 5 amp or less charger for maybe 12 hours and then see what happens.

IF.....the onboard system is/was charging it at 14.9 ALL the time, it likely damaged the old battery.....and will do the same to the new one too.

A totally healthy, fully charged AGM battery should read 12.8 or maybe even 12.9.
And then sitting overnight with no load or a tiny load should not go below 12.6.

 

I watch my system voltage to and from work and around town. I see a voltage of 13.96-14.01 reported by my OBD device. I just put a new battery in the week of Thanksgiving.

 

If it does not drop to 13.x it means the battery isn't charged enough yet. The dc to dc converter in the inverter has an elaborate charging algorithm like the best chargers. I would get a maintenance charger and ensure the battery is desulfated and fully charged. AGM Batteries And Testing -

 

That is because it is NOT right.
Your battery needs to be tested......thoroughly.
If the "system" thinks it is very low on charge, it can charge at that voltage for a a short time but ONLY a short time.
Second time saying this.

 

And batteries fail MUCH more often than the charging system does.
It is likely that battery will NEVER charge "enough".

 

i would focus on the parasitic current. If it is "1A +- 0.2A" that is way too much. It should stabilize from 20ma to maybe 90 ma. One owner right now is trying to reduce his measured 90 ma. Make sure the hatch light is not staying on and no odb2 adapter is left plugged in. I might run the negative battery amp draw test leads outside of the hatch with a meter in circuit to verify the actual current after an hour. If still high get somebody to fix it. That much parasitic amp draw can kill your new battery in a relatively short time.

If it is a choice between a bad battery or a bad inverter charging circuit, the odds are your new battery is defective.

As far as a fuse to pull for two weeks, there really is not an easy one. The overall fusible link is in the battery positive terminal and is bolted in as is the engine fusible link block. Even if you simply disconnected the battery negative you would still have an issue opening the hatch manually from inside.

The best option for one day or two weeks is a good lithium jump pack in the cabin plus resolution of the parasitic draw issue if it remains high. At that point, with a good battery, it will start after two weeks without you disconnecting anything. Personally, I have parked three weeks at the airport without disconnecting anything and had no issues. It was a Toyota battery which lasted almost eight years.

If the car is stored at your house, I would absolutely put a Battery Tender Jr on it to ensure ensure a charged battery. If you can't use a charger and want to disconnect the negative lead, a jump pack or a small alarm style agm would be enough to power the system and allow the electric hatch lock to work. Of course, if you do disconnect, use the mechanical key inside the keyfob to enter and open the hood.

 

We see a range of 14.1V - 14.9V and 0.1A - 1.0A depending on (low) no-load or (high) cabin device charging load.

 

OR SUCH.....would certainly include an after-market remote start I would think.

 

i don't know about revving the engine, but prius is not a good battery charger. more of a maintainer.

 

Agree.

 

It is kind of sad when a Toyota service advisor tells you to rev your Prius to charge the battery. And "don't worry, the battery has a long warranty". Obviously they are more salesmen than techs.

Are you using your clamp-on dc amp meter to measure standby milliamps? DC clamps are usually not real accurate below an amp unless it is a high dollar Fluke or equivalent. Most of us break the negative battery lead and use a meters internal amp shunt. Its tricky because the initial surge may be over 10 amps so its a good idea to jumper at first, wait a few minutes and then disconnect the jumper. See pic.

0.3 amps (300ma) is still too high. A back of the napkin calculation gives you about 3 days on the safe side. I will check my car in the next couple of days and give you my draw.

The calc I use takes half of the amp hour capacity divided by the parasitic draw. That gives you the number of hours. Then divide by 24 to get the number of days. So the Toyota battery is about 40 amp hours, divided by 2 equals 20 amp hours usable. (20 / 0.3) / 24 = 2.77 days.

At 35ma it is (20 / 0.035) / 24 = 23.8 days. Big difference.

 

There is a main 12v feed that comes to the engine fuse box. I am sure it is bolted on from the bottom to the fusible link block in that fuse box. You might dc clamp it as it goes into the box. It should be ~1/4" diameter but I have never had a need to find it on my gen3. This box feeds the interior fuse box.

I would try the direct meter shunt method. I have a couple of dc clamps and they don't work well at low ma and read high. You don't want to chase a ghost.

The charge voltage should not be a concern. If there is a big drain the inverter's dc to dc is just reacting to a low charge level. It does have a dc sense input but no battery temp. There is a big fusible link in the positive battery terminal.

The inverter does not fast charge the 12v battery. AGM batteries don't cook like normal lead acid batteries and are more forgiving of moderate discharges from a longevity standpoint.

Toyota sells online and downloadable reference material at their TIS site. Two days are $20. Electrical is many separate docs but once you get there download as much as you can.

Find the remote start and remove it. My guess its in the interior fuse box.

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