I recently bought a used '09 with 107K miles. Even if I am super light on the gas pedal, I have never been able to remain on battery power past 10 MPH....maybe15 if I'm going down a hill....never touched 20. Is this a sign the battery is on it's last legs? If I can get up to 30 MPH as advertised, I would get crazy high MPG on my commute.

 

Please be aware that the usable energy in your HV battery is LESS than the total energy stored in the 12V battery under the hood.

To illustrate my point:

12V * 70Ah = 0.84kWh
288V * 6.5Ah * 40% = 0.75kWh

Imagine how absurd it would be to expect to propel your vehicle purely on the energy stored in the 12V. You would not expect to go far at all.

You do not have an EV.

You have a gasoline powered vehicle with a kinetic energy recovery, storage and release system designed to improve the efficiency of the gasoline propulsion system. 100% of the energy used for propulsion of your vehicle ULTIMATELY comes from gasoline.

To your question, 30 mph is a highly idealized number where your rate of acceleration is so slow, you will completely p!ss off everyone behind you. You must not be using any unnecessary electrical power, nor can you be using the A/C or heat, and you must be on flat/downhill terrain. Furthermore, you have to start the EV run when the battery is higher than its "target" state of charge like after a long deceleration or at the bottom of a long down hill where the battery is charged to the high end of the operating range. The 10mph is more indicative of typical operation. However, if you find it impossible to achieve higher speeds in pure EV mode, you are likely looking at a deteriorated battery.

If the car is running and performing normally, and you can attain the EPA rated mpg without extraordinary effort, it is likely not a sign of impending battery failure; however, it is a certainty that your battery is significantly deteriorated from when it was new and likely has a relatively small available capacity. The GM hybrids are very hard on their batteries.

 

Thank for the reply Keith. I was just curious if the advertised 30 MPH was the norm. I knew that, if it was possible, that you had to be feather light on the gas. I have tried to do this when there was no one behind me, but never had any success so was worried something was wrong with the battery capacity. The way it was advertised was that if there was enough battery charge, the car would run purely on electric and get you up to 30 MPH before the gas engine would need to kick on.....again IF you don't accelerate to hard. I guess, like EPA mpg ratings, that this is best case, nearly impossible to get numbers. I have been running the heat in auto mode and will try to test the car with EVERYTHING off next time to see if I get better results.

Outside of that, the vehicle seems to be operating normally. Engine drops from 4V to 8V fine and, knock on wood, no fault codes. I haven't had a whole lot of time behind the wheel with it, but I am seeing about mid-17's as an average in mostly city miles. My Durango Hemi gets 13.1 on the same route so it's an improvement.

 

According to fueleconomy.gov:

https://www.fueleconomy.gov/feg/Powe...oe&srchtyp=ymm

City is 20-21mpg.

 

Winter cold is hard on everything. At around 28 mph even rolling down a hill, that engine is going to start. Long discussion about power here.


You have to be very good and steady on the pedal in these and a Prius to accelerate above 25 mph in times faster than a Sun Dial measures.

 

This is my baby right here now....

This old Tahoe Hybrid makes me smile every time I jump in in to drive off.....................
Interesting thread. Just for comparison my 197,000 mile 2009 TaHoe Hybrid with original traction battery reaches +20mph easily with light gas pedal pressure before the engine kicks on even with heat on high/both heated seats on and rear defogger running etc. (28f here this morning) The electric motor in these must be pretty large as I can get decent acceleration right off the line too. + I am at a big disadvantage with a 3.5" lift kit/oversize wheels and big knobby offroad Nitto Grapplers. Averaging 18.3 MPG in mixed city/highway driving. I love this Tahoe Hybrid the tech fascinates me and I bought it so cheaply that even if all the wheels fall off tomorrow I would still be OK with it LOL.
I guess later model vehicles have improved fuel efficiency. I have a New 2018 GMC Sierra 1500 Denali Ultimate "pic at top" with the 420hp 6.2 that has averaged 21.6 MPG over its first 6,000 miles (0-60 in 5.4 seconds)