Robotic lawnmowers and thunderstorms: what can happen?
Thunderstorms can cause problems for your robotic lawnmower in several ways. In a particularly bad thunderstorm it is possible that it may knock out the charging station or the circuit board inside the charging station. As the vast majority of robotic lawnmowers today utilise a boundary wire and guide wire installation, it is comparable to having a large conducting antenna in the lawn. The lightning tends to be caught in the live cable and causes damage to the charging equipment when the voltage becomes too high.

What usually happens?
If your robotic lawnmower has stopped working after a thunderstorm, it is usually one (or more) of the following three things that have happened:
1. The lightning has penetrated the boundary wire and caused an overvoltage which has damaged the circuit board.
2. The lightning has passed through the boundary wire, which in turn has caused damage to the transformer.
3. Lightning has hit the robotic lawnmower or charging equipment, causing damage.

The most common of the three is 1, or 2. It is very rare that lightning causes damage to the robotic lawnmower itself. In the event of a malfunction occurring after a thunderstorm, it is more likely that the charging equipment has been damaged. 

The fault is identified by the robotic lawnmower no functioning with the warning light "no cable signal". The first thing to do then is to check which of the lights in the charging station is activated.  
If the lights in the charging station are completely off, it may be due to a problem with either the transformer or the circuit board in the charging station. We recommend that you first measure the transformer's voltage output.
The transformer is marked with the number of volts it should produce. Measure and check. If the transformer is delivering the specified voltage, it is very likely that the circuit board is defective.
The next course of action is to replace the circuit board in the charging station.

 the transformer does not produce any voltage at all or produces a voltage lower than specified, the transformer is most likely defective. The next course of action is to install a new transformer.

 If the robotic lawnmower has been subjected to lightning strikes, it should be returned to an authorised dealer for inspection and troubleshooting as there may be several faults.

How to protect the robotic lawnmower from thunderstorms?
We have not yet found a lightning protection system that works satisfactorily and protects all the components. There are several variants on the market but either they protect only the charging station or the transformer. In some cases, they do not work at all against the potential surging that can occur, making them useless to the user.
There is also no lightning protection on the market that can handle a direct hit (lightning) on the charging station. It is simply too big of a force.

Our advice would be, wherever possible, to unplug both the transformer from the wall and the boundary wire from the charging station. That way you've protected yourself as best you can

Husqvarna is expecting to launch a lightning protection system in 2023 that will protect both the charging station and the transformer.