Can I Use More Than One Battery Pack in a Honeywell L5100?

No, you cannot use more than one battery pack in a Honeywell L5100. Trying to use multiple battery packs could cause damage to the panel. The system relies on its backup battery to remain powered on if the the electricity goes out or if the plug-in AC transformer becomes disconnected.

Even though the L5100 actually has two available backup battery connector ports, connecting two backup batteries is a very bad idea in practice. The reason the system has two battery ports is to accommodate backup batteries with two possible connectors. The smaller connector port supports the LYNX Touch Standard Capacity Battery and the LYNX Touch High Capacity Battery. The larger port is for the LYNX Touch Super High Capacity Battery only.

One might think that they could connect a Super High Capacity Battery in the larger port and use it alongside either a Standard Capacity Battery or a High Capacity Battery in the smaller port. But doing this can cause serious problems. For one, only one battery can physically fit inside the panel. The other battery would be forced to dangle from the outside. Using multiple batteries can also overload the system's board and result in permanent damage. Having two batteries can also drain too much AC power, and the panel might display an AC power loss condition as a result.

The longest lasting backup battery for the L5100 is the Honeywell LYNXRCHKIT-SHA. This is the Super-High Capacity model that connects with the larger battery port. It can keep the L5100 running for up to 24 hours on end. If a user expects that they may lose power for more than 24 hours, then trying to use multiple batteries is not an appropriate solution. Instead, they should look into getting an external generator to keep their system running on AC power even when conventional electricity is lost.