Went from 42 to 46 MPG with some hypermiling techniques!
 

I've been on this forum on and off but recently bought my mom's 2008 Civic a few months back. The battery was in terrible shape, recals every 5-10 minutes and only getting about 32 MPG. I noticed that the 12v battery was completely toast and it was starting from the hybrid battery every time. I replaced it with a new battery for a regular Civic, which is a bit bigger, and that instantly bumped the MPG into the 35-36 MPG range. Then I moved to a job with a longer highway commute and that bumped it up to ~38 MPG and it stayed there no matter what I did. I built a cheap grid charger and noticed the benefits right away, but it only stayed good for half the day, then it would recal all the time again. At this point it was getting close to 39 MPG. So I spent a weekend doing one charge-discharge-charge cycle and that got my MPG up to 42 and has been there up until now. It didn't recal for 3 days, and then only does one recal per drive when the engine is cold. That was about 2 months ago and I've plugged in the grid charger overnight every 2-3 weeks. It won't recal for a few days and then just does one recal a day after that.

I've been redea up on ways to improve MPG and incorporated the following into my commute this past week:

• Driveing with load/target driving - speed up down hill and slowly let off the gas uphill to try to stay at a more constant MPG. I'll speed up to 70 mph downhill and will get down to as low as 58 mph up hill. I try to time is so I'm down to about 60 mph at the top of the hill. My goal is to stay at 50+ MPG but it does dip lower on some longer hills.
• Drive without brakes/timing stops and lights/conserving momentum - This goes for both freeway traffic and city driving. I keep a long distance so I can let of the gas and slow down with regen braking. By the time I get close to a light or car, it hopefully moves again so I never have to come to a complete stop.

I just filled up 10.5 gallons after driving 488 miles on this tank, for an MPG of 46.47! Same pump I always use so it should be fairly accurate. I'm going to continue and see if I can get 45+ for the next tank as well.

I'm pretty impressed at this point, and I'm due for new tires soon so I'm excited to see what Ecopia 422 Plus tires will do for me. Currently the car has some Mastercraft tires on it. If the tires bump my MPG, I'll probably keep grid charging and driving the car until I can't get 40 MPG out of it and look at getting an upgraded Bumblebee battery because 2k is cheaper than buying another car.

Any other tips you guys have? I'm not going too extreme like smooth wheels or mirror deletes but I've been considering a block heater since my commute starts in <40 degree weather for a good 4 or 5 months out of the year.

Re: Went from 42 to 46 MPG with some hypermiling techniques!
 

Not bad. I was able to consistently get north of 50mpg if I made myself miserable by not using the A/C and practicing very similar hypermiling techniques. I also stabbed the throttle off the line to get max assist, then held 2K rpm and accelerated.

Here in AZ, this also had the amazing side effect of completely destroying my battery. When you're pulling in 110°F air to cool a hot battery... yeah... dumb. Don't be me.

You might notice no improvement or even a slight drop when you first put the EP422 on. They can take 1-2K miles to "break-in". You'll likely get 1-3mpg improvement.

Grid charging at temperatures below freezing is not particularly productive unless you do it for a couple days or install a space heater in the interior to bring the temps above freezing.... preferably above 50°F.

Re: Went from 42 to 46 MPG with some hypermiling techniques!
 

I forgot to mention that I commute to work at 1AM and go home at 10AM. This is on the PNW so there’s only a handful of days per year that I might want A/C. I’ve seen that stabbing method mentioned here but my battery is too weak to do. I’ll lose like two bars quick if I try that. I do accelerate fairly quick because I think it gets me better overall MPG than taking a whole minute to get up to speed.

The MPG drop with the tires isn’t new to me. We saw a solid 5 MPG drop on my wife’s Prius when it first got new tires.

Good to know about the temperature for charging. I don’t think I’ve done it in freezing weather yet but definitely under 50 degrees. I did notice something with the last charge I did. I checked on it and it was up to 185v or so after almost a day. I left it on until later and came back to a 178 voltage. Left it on for another 4-5 hours and it stayed at 178. Any idea why it would drop like that? Car also acted funny for about an hour, IMA fans were on at full blast and I had no charge or assist. Once the fans turned off full blast, it was back to normal. Maybe it was overheated? The fans are on for the charge cycle.

Re: Went from 42 to 46 MPG with some hypermiling techniques!
 

When a battery hits 100%, it's voltage naturally drops. It's a Nickel thing. Compound that with heat, and you get another bias for lower voltage. 7V is a pretty big drop. That plus the fan behavior pretty much guarantee you got that battery REALLY warm. That definitely won't help its life, and it will rapidly necessitate discharges to recover lost capacity.

For future reference, if it ever drops more than 2V from peak, stop charging. You may want to provide a means of continuing cooling AFTER you've stopped charging.

Given the frequent need for grid charging, and the "overnight" charges, you're likely pushing the healthiest cells to 100% and heating them up while the weaker cells never hit 100%. IIRC, your fan duty cycle is adjustable. Once you're over something arbitrary like 180V, push the fan to max. You may notice your peak voltages INCREASE with additional cooling.

Next to last, it might be worth monitoring the IPU exhaust for temperature. If it hits 100°F, time to stop charging.

Lastly, you always have the IPU lid firmly in place and sealed when charging, right? We've probably already discussed that, but I can't remember squat.

Re: Went from 42 to 46 MPG with some hypermiling techniques!
 

You must’ve discussed this with someone else. But now that you mention it, I did have the lid off for this last charge cycle. Is it required for cooling?

Re: Went from 42 to 46 MPG with some hypermiling techniques!
 

IPU lid off = ZERO cooling.

IMA fan blows air into the trunk SUCKING air in through the inlet on the rear deck down through the pack. With IPU lid off, you were just sucking air in from the back seat.

The rubber seal gives a near air-tight seal when the IPU lid is properly installed.

Highly likely you did some damage. A 24 hour charge followed by a discharge to 96V is in order.

Re: Went from 42 to 46 MPG with some hypermiling techniques!
 

Started my charge last night. It was 186v early this morning, 188v now. Do I wait 24 hour no matter what or should I stop it when I see the voltage drop a bit?

After the discharge to 96V and then another re-charge, would it be worth doing an even deeper discharge?

Re: Went from 42 to 46 MPG with some hypermiling techniques!
 

In most cases, a HCH2 battery will peak at above 190V when fully charged. Access the IPU exhaust behind the passenger side trunk trim panel. If the exit air is 95+°F, then terminate charge. Otherwise, termination criteria are:

24 hours
holds peak voltage for 8 hours
(the above two are preferred)
drops 2V from peak
Drops any amount 8 hours after hitting a peak.

Discharging when all 132 cells aren't at 100% charge runs a very high risk of destroying any marginal cells that might otherwise have some life left.

AFTER any manual discharge, MANDATORY 24 hour charge. Period (mostly). If you have urgent need to use the car, charge for 4 hours minimum, disconnect 12V, start and allow the car to charge at idle until it stops charging.