Civic Hybrid batteries in series

I own a 2008 Honda Civic Hybrid. My commute home is long and up hill and the hybrid battery runs out of juice half way up the hill.
My question is…
Is it possible to have 2 hybrid battery packs connected in series?

Not really, your hybrid system is optimized around the current battery/engine/electronics, no way to just plug in an additional battery.

Are you sure your battery is in good shape? Do you get the same mpgs as before? How long have you owned it? After 11 years you could have some failing cells. Honda’s hybrids have been more troublesome.

And no hybrid will keep powering a car on an extended uphill, that’s what the gas engine is used for.


I have owned the car for 2 months. I bought a battery pack with new cells from Greentech Auto a month ago.
I am getting 48 mpg. When the battery stops assisting the engine on an up hill then I have to rev the engine higher to keep the same speed and use more gas. I just wanted more mpg and was wondering if there was a way to boost the capacity by having two battery packs in series.
Thank you for your reply and I appreciate you help and info.

Maybe you should get the hybrid battery pack tested to make sure it’s not defective. I’m disappointed the car doesn’t appear to be intelligent enough to learn your commute pattern and ration battery power accordingly. Except for the original Insight, Honda’s hybrids never quite measured up to Toyota’s, so it’s not the hybrid I’d have chosen to buy used.

Connecting them in series would boost (double) the voltage not the capacity. You’d roast the control and drive electronics. To increase capacity, you’d need to connect them in parallel. Assuming you could overcome the technical difficulties, this would not make much financial sense to do as the ROI would be unfavorable IMO…


I don’t think any hybrid does this. Mine just reacts to the combination of load, throttle, and remaining battery charge.

That’s disappointing. What about an electric Tesla? You’d think they’d have intelligent software for the price.

I also wonder about how the added weight of a second battery pack would affect the car’s performance. The loss in efficiency would likely outweigh (no pun intended) the advantage of extended range.


When the Prius was ‘new’, some companies tried to come up with add-on battery packs to do just what the OP wants to do. Not only were they financial failures (cost lots of money), they didn’t result in much of an improvement in mpgs overall. It takes LOTS of work to optimize such a complex system.

You are correct in series vs parallel that is the way the 2 batterey’s are hooked up in diesel truck’s

Especially climbing a hill!

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Where would you put a second hybrid battery anyway ?

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It’s a Civic, so there should be trunk space.

I’m always fascinated by the un-credentialed people who think that they have better engineering skills than the people who designed a vehicle.

Hot Rodders do it all the time. They are able to do it for specific purposes and are not constrained by the myriad requirements the factory engineers must meet.

Pontiac never built a 400 mph car but Mickey Thompson took 4 Pontiac engines and made a car that did.

… and they also don’t have to balance performance with reliability/durability.
The folks who engineer and test new cars prior to production must do their best to make them “idiot-proof”, so that purchasers who are not car-oriented don’t destroy the vehicle… at least during the warranty period. Hot rodders–who are looking for maximum performance, and who enjoy turning wrenches–don’t have that type of constraint, and it results in a world of difference.

The sun is also setting on the ability to “hot rod” a vehicle in the traditional sense. Onboard diagnostic monitoring and periodic inspections already constrain the freedom to change now. I predict it won’t be too long before the electric car CBL (check battery light) includes diagnostic checks for compliance to the original specifications in much the same way conventional ICE cars are doing now. Not to mention showing up for your annual inspection with an unapproved auxiliary battery pack stuffed in the trunk… :stuck_out_tongue_winking_eye:

You do know that there are large chunks of the country that do not have inspections.


Adding a second battery could theoretically be done.The practical problem is that adding another battery – besides needing space somewhere to put it – would require modifications to the car’s drive-train electronics package. If you can find a vendor that offers both the battery and the electronics package, might be worth a try. Be sure to get permission from the state DMV and your insurance company before considering this.

This is a multi-thousand dollar project to maybe save a few hundred dollars in gas, at most.

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