Portable car batteries and chargers aren’t significantly regulated and as Consumer Reports has noted, some manufacturers’ performance claims are dubious. Always read the fine print. For safety, look for batteries that are certified for compliance with Edison Testing Labs/Intertec or UL standards.
Always think about temperature. Manufacturers recommend not storing batteries in high-temp environments. If you want to keep a battery in your car, keep it out of direct sunlight in the glove box — or better — the trunk. In the summer months, it’s better to grab it when you start your trip and take it out of the car when you get home.
Then there’s the other extreme. Anyone vaguely familiar with batteries knows that they’re not terribly fond of extreme cold. Consumer reports found that when both the jump starter and the weak car battery were cooled to zero degrees, the performance of even the best portable jump starter options degraded significantly. If it’s really cold out, warm the portable battery indoors or inside a car first and keep it as warm as possible before you use it to jump a vehicle.
Chemistry does matter when it comes to the care and feeding of a car jumper. Conventional sealed lead-acid cells are heavier and discharge more rapidly than lithium ion batteries when they sit idle, but they can also be less sensitive to temperature extremes and to significant physical impacts. Either way, the care strategy with sealed lead-acid or absorbent glass mat is straightforward. Keep the battery charge as close to full as possible as much of the time as possible.
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