New to forum - battery question

I'm sorry I didn't think to look for this forum before. I have my MIEV for about two months now. On my first night home with it I didn't plug it in and the next morning it was dead. My charge was down and the dash showed the outline of a battery. A full charge fixed it, of course. That night on the way home I'd had the AC on along with the radio and lights. Since then I've been careful to keep the use of those things to a minimum. A few days ago, however, I took three friends on an outing and they were uncomfortable, so I used the AC most all of the trip. The next day my charge showed half, but the red battery pic was on the dash, and the car was dead. A full charge fixed it again. But I need to understand what draws on what battery and how to tell when the small battery is going down. Can anyone help?

The small battery (also called an auxiliary battery, since it powers the non-essentially items in the car) is just like the battery in any other gasoline car and provides power for switches, the radio, windows, locks, ect., but not the air conditioning or heating. Those draw too much power. The main battery (also called a "traction" battery because it provides the traction to the wheels on the road) provides power to the climate controls AND, incidentally, to recharge the small battery. Ultimately, all energy is coming from your main traction battery.

If you drive the battery down too far you will get the "---" range remaining and the turtle light. Upon charging back up, as you've noticed, all you're doing is recharging. If the red battery light is lit, it indicates some problem with charging or possibly a problem with the auxiliary battery. If this happens repeatedly, you should take the car to the dealer, perhaps there is a problem. I have seen it on my car during a charging error, but only rarely.

Finally, you should not drive your car repeatedly until the range remaining says "---", that is both a bit nerve-wracking and bad for the battery. Normally you should consider the last bar or two (5-10 miles range remaining) as empty and you should recharge at that point.

Do you have the faster charging at home or are you only using the charger that came with the car? I have found that using only the charger that came with the car is just too slow if I get home late at night sometimes and then want to head out on a normal day the next morning. To recharge from empty to full takes 22.5 hours on the charger supplied by Mitsubishi.

Several things you must consider when driving your electric car:

1. Driving distance. If your round-trip is over 50 miles, you may have to charge along the way.

2. Accessory usage. If you have the A/C running, it's going to reduce your range. The heater reduces your range even more. Rear defroster? Yep, reduces range. Keep accessories off or "low" to keep range reduction to a minimum.

3. Load. How many people do you have in the car? How much cargo? Weight reduces range.

4. Charging rate. If you're using your L1 charger (the 120V charger that came with your car), a full charge will take overnight and, if the battery is really low, longer. You will need an L2 charger if you're frequently running your battery down to low. Charge your battery whenever you can. When you get home, plug in your car. Charging at your destination is a good idea when possible too.

5. Aggressive driving. Keep the ECO meter near the first notch when accelerating to maximize range.

6. Highway driving. Due to aerodynamic losses (air pressure against your car), high speeds use more power than low speeds.

Now, if your car is completely "dead" (e.g., you can't drive it), your secondary battery could be at fault. Your car has two batteries: The large one to drive the car and a small one to run the electronics and computers. Take your vehicle to the Mitsubishi dealer and have them check the small battery. Let them know you get the red battery warning overnight.

FloridaJanet - the red battery light means something is wrong. My guess is either your 12V auxilliary battery is bad or the DC/DC converter has a problem. I would take it to a dealership to have the car inspected. I've run my car almost completly flat of charge (turtle and "---") and never saw the red battery light come on. The 12v battery is obviously not completely dead or you wouldn't even be able to charge, something else is amiss. Have it checked out and let us know what the diagnosis is.

Welcome to the forum, Janet - Glad you're here!

MLucas said:

FloridaJanet - the red battery light means something is wrong. My guess is either your 12V auxilliary battery is bad or the DC/DC converter has a problem.

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My thoughts exactly. I'll bet they'll replace your 12 volt 'starting' (auxiliary) battery and that will fix it. I've read about two other cars which experienced the same problem

Don

Thank you everyone. I am just back from the dealer with a new battery installed. The battery was rated 270 and mine tested at 48! It was probably bad when I picked up the car in February. They said that is not unusual here in Florida as just sitting in the heat wears them out. I do hope that doesn't happen with the big one before my lease is up in two years. I have only a carport for keeping it cool. I have set a box fan out there to give it a breeze on the extra hot days. Don't know if that will help or not. The manual says to keep it in temps under 77. Wonder why they sell such cars in Florida. Most of the year we hover around 90! Thanks again.

Janet ... great, glad you got the battery issue resolved. I wouldn't bother with a box-fan to cool your car. If you keep it in a carport on hot days, that should be ok. The car has its own fan specifically for cooling the batteries, and will do this while charging (you'll notice the sound sometimes immediately after plugging in). It can also use the air conditioning air to help do that in summer. If you have the Quick Charge port (and perhaps without it too, I'm not sure), the iMiev website says: " ... we've added an air-cooling system that draws cold air from the air conditioning unit to keep the battery nice and cool, even in hot climates."

So, though Florida is hot, I'm thinking it would be a very good place for an EV, since cooling is less of a demand than heating (which you don't have to worry about), and it's very flat. Where I am, I routinely travel up and down 200-300ft hills several times in a 10 mile one-way trip.

FloridaJanet said:

Thank you everyone. I am just back from the dealer with a new battery installed. The battery was rated 270 and mine tested at 48! ...

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Hi Janet, and glad you had your battery issue resolved. Just to be clear, the battery you had replaced was the small 12v auxiliary battery and not your large traction battery pack. If a car sits unused for a long time (e.g., on a dealer's parking lot), that small battery gets depleted due to standby currents (e.g., alarm system). Deeply discharging such a small 12v battery and letting it sit there 'dead' is tantamount to murder of that battery and even if the dealer drags over a booster charger and gets it going again, that small battery's lifespan is significantly shortened. Most modern cars have this problem (not restricted to electric cars) but the 12v starter batteries in larger cars have a larger capacity and are better able to withstand a gradual discharge of a few months of unuse. For our iMiEV, we don't need a large 12v battery at all because we do not have any need for the high-currents that ICE cars require to grind engine starters in sub-zero weather.