Mixing Battery Sizes
1. Understanding Parallel Battery Connections
So, you're thinking about hooking up a 12V 50Ah battery alongside a 12V 100Ah one? It's a common question, and the short answer is: it can be done, but it's usually not the best idea. Think of it like this: you're trying to have a relay race, but one runner is a sprinter and the other is a marathon runner. They can both run, sure, but one will likely be dragging the other down in the long run. Let's dive a little deeper into the whys and wherefores.
When you connect batteries in parallel, you're essentially creating a larger battery bank with the same voltage (12V in this case) but with a higher overall capacity (measured in Amp-hours, or Ah). This means you can power your devices for a longer time. But here's the catch: the batteries need to be relatively similar in terms of voltage, chemistry, and state of charge to play nicely together. Otherwise, you might end up with some unintended consequences, like one battery constantly trying to charge the other, which can lead to reduced lifespan or even damage.
Imagine two water tanks connected by a pipe at the bottom. If one tank is full and the other is half-empty, water will flow from the full tank to the half-empty one until they're at the same level. Batteries are similar. A battery with a higher voltage (or a higher state of charge, which translates to voltage) will try to "charge" the battery with the lower voltage until they equalize. This equalization process, while normal, can be problematic if the batteries are significantly different in size or condition.
The key here is balance. You want your batteries to work together, sharing the load and charging evenly. When you introduce mismatched batteries, you're throwing that balance off. A 50Ah battery has a different internal resistance compared to a 100Ah battery, which means it will react differently to charging and discharging. This difference can lead to stress on the smaller battery, potentially shortening its lifespan. It is always better to use batteries with same Amps.
2. The Potential Problems of Mismatched Batteries
Let's spell out the specific issues you might encounter when paralleling a 12V 50Ah battery with a 12V 100Ah battery. First, you have the potential for uneven charging and discharging. The smaller 50Ah battery will reach its full charge faster than the larger 100Ah battery. Similarly, it will discharge faster. This disparity puts extra stress on the smaller battery. Think of it like constantly overworking the little guy.
Next up is reduced lifespan. Repeatedly stressing a battery beyond its designed capacity inevitably shortens its lifespan. The 50Ah battery, constantly being pushed to its limits while the 100Ah battery loafs along, will likely degrade much faster than if it were paired with a similar battery. So you are not actually saving money doing it.
There's also the risk of overcharging or undercharging. If your charging system isn't sophisticated enough to handle the differing characteristics of the batteries, one battery might get overcharged while the other remains undercharged. Overcharging can lead to gassing, bulging, and even explosion (though that's rare), while undercharging can lead to sulfation and reduced capacity.
Finally, consider the overall performance. While you might think you're getting the combined capacity of 150Ah, in reality, you're likely getting less than that. The weaker battery can drag down the performance of the stronger one, resulting in a system that doesn't perform as well as it should. It is advisable to make sure batteries are not too far apart in terms of Ah.
