We actually replaced our 12V with a dealer-sourced replacement a couple months before the plunge in FE.

Interesting that some other threads suggest a linkage between this 12V and FE. Does the HCH have an alternator to charge it? Since it functions as the backup to start the engine, I guess I just assumed it was charged from the engine vs. the hybrid battery.

I think I'll go ahead and change back to Honda's 0-20W oil (+2-4 mpg would pay for it). Have seen some other posts saying this is a synthetic blend, and that adds credence to the notion that Honda had some benefit in mind in specifying a unique type of oil for the HCH application.

We still like the car as a 36 mpg vehicle, but the real loss is the battery charge falling to the point that there's no more IMA assist. It's a bit of a safety risk really, as the engine by itself produces much less acceleration and someone like my wife might not realize there's no IMA assist available when she goes to pull out into fast-moving traffic.

 

The IMA battery charges the 12v battery. A weak 12v battery will place a higher draw on the IMA battery to keep it charged, leading to a persistently low IMA charge.

As an experiment, I connected my HCH II to a trickle charger overnight for a week before I got a new 12v. My mileage improved notably. Even my new battery, a deep cycle Optima, shows a difference.

 

Thanks for the information. I assume the deep cycle Optima is a third party battery rather than sourced by Honda? Do you know if you are getting better mileage with the Optima compared to the Honda battery when it was working properly?

 

My headlights definitely seem brighter, and since I have fog lights I don't think the battery is under such a load that it's constantly trying to play "catch up." Is long as a smaller Optima (D51R) is used, it should give better mpgs. On conventional Civics, some owners use a D35R, which is a bigger battery or a red top Optima starting battery rather than a yellow top deep cycle battery. This, however, can draw more on the IMA battery to keep it's charge (since it's bigger) and have the same net effect of a low IMA battery.

The Optima is a deep-cycle battery like the Honda is (in theory, at least on the Honda's part). Since lots of accessories are driven off the 12v battery, a battery that can deep cycle will last longer and give improved vehicle performance and battery performance. I got my D51R for ~$140, whereas a replacement Honda battery was ~$112. If you live near an online retailer you can get a Honda battery for as low as the $70-80 range when I checked about a month ago, though I could not find a Honda accessory retailer that would ship a 12v battery. Optimas can run into the $160 range. However, they last much longer than the Honda 12v battery, which is good for 3-4 years at best, hybrid or not, and give improved performance with brighter lights, less drain, etc. I also top mine off occasionally (once to twice a week now) with a trickle charger, which will help to lengthen the battery life even longer. I do this for my HCH II and my wife's 2010 Insight.

That's whats wrong with going to Auto Zone or Wal Mart and getting any old battery. They are usually great for starting, which is useless to us since our cars almost never use an actual starter, but discharge quicker, thus needing a recharge form the IMA more often and lower mpgs.

I'm no electrical engineer, but I hope this helps...

 

Hi medicmike,
Thanks for the information. You sold me on getting an optima battery when my Honda battery needs to be replaced.