![]() If you have an 85-milliamp draw in a car with just a single 50Ah battery, as is the case in most vehicles that aren't diesel trucks, your battery will be completely discharged from a full state of charge in just over three weeks. While these timeframes all seem more than reasonable for a typical vehicle, don't forget this truck is running two batteries. If the parasitic draw went up to 85-milliamps, the math works out to 2.04 Ah per day, which would accelerate the discharge rate to a 0% state of charge by 20 days. That timeframe can also be shortened significantly if there are any additional accessories that may draw current with the key off, like an alarm or even a cell phone charger. The batteries also need to be well above a 0% state of charge to start the truck. That timeframe also can be shortened in hotter climates or extended in more temperate climates. If the batteries are not fully-charged, that timeframe can be shortened significantly, depending on the state of charge. That means if the truck is parked with new, fully-charged batteries (most are not), it will take just under 70 days (100/1.44= 69.4) days for the truck to completely discharge both batteries. If the parasitic draw is 60 milliamps, that means it will discharge the batteries at a rate of 1.44 Ah per day (.060 x 24 hours). ![]() That's not too bad, considering I have some of the newer electrical accessories, like memory seats, mirrors and radio presets, but how long can this truck sit before it completely discharges the batteries? This truck is equipped with two Group 34/78 REDTOP batteries, which means it has 100Ah of reserve capacity. I did just that today and it indicated a draw of about 60-milliamps. Although I have checked the parasitic draw on my Excursion in the past, I'd never photographed that test. In fact, we suggest a 25-milliamp draw is acceptable and anything that exceeds 100-milliamps indicates an electrical issue that needs to be addressed. In that same conversation, it was suggested that a 200-milliamp draw was "acceptable." That is certainly not the case. That is why vehicles that only see weekend or occasional use (this includes boat owners) should have their batteries maintained with a quality battery maintainer, like the OPTIMA Digital 400 or Digital 1200 Charger & Maintainer. When that happens, sulfation begins to diminish both capacity and performance. ![]() The combination of a significant parasitic draw and long periods of non-use can easily cause voltage to drop below 12.4 volts. The key to long life for any battery is to make sure battery voltage doesn't drop below 12.4 volts. ![]() ![]() If a vehicle is driven daily, the alternator should probably have no trouble properly maintaining the battery, provided that daily use doesn't consist of a multitude of five to ten-minute drives. Until the day comes when battery maintainers are standard equipment on all new vehicles, we just need to be vigilant with our batteries. As even more electronics are packed into newer vehicles, those trends are both likely to continue. Some high-end exotics even come with battery maintainers as standard equipment. Some automakers have responded by shipping their vehicles with solar chargers, to keep the batteries charged as much as possible between the time the cars leave the factory and when they arrive at the dealership. However, just because an 85-milliamp draw may be normal, that doesn't mean an 85-milliamp draw won't adversely impact battery lifespan and performance, if the battery isn't properly-maintained. Memory seats, mirrors, radio presets, satellite radio, GPS systems, Wifi and lots of other fancy electrical gadgets have combined to greatly increase the electrical demands of many newer vehicles. As I explained the math behind parasitic draws, it was suggested that an 85-milliamp draw is not all that uncommon on newer vehicles. I was having a conversation recently on an Internet message board, when the subject turned to parasitic draws or "key-off" loads. ![]()
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