Update customisation.md

docs/customisation.md

@@ -254,9 +254,15 @@ you want to export as late in the day as you can.
 **input_number.predbat_best_soc_keep** is the minimum battery level in kWh that Predbat will to try to keep the battery above for the Predbat plan.
 This is a soft constraint only that's used for longer term planning and is ignored for the forthcoming first 4 hours of the plan.
 As this is not used for short-term planning it's possible for your SoC to drop below this - use **input_number.predbat_best_soc_min**
-if you need a hard SoC constraint that will always be maintained.
+if you want to force all charges to be above a set level.
 It's usually good to have best_soc_keep set to a value above 0 to allow some margin in case you use more energy than planned between charge slots.
 
+**input_number.predbat_best_soc_keep_weight** (_expert_mode_) Is used to tune how strongly you want the keep metric to apply. 
+A value of 0 would essentially ignore keep while higher values will make it more important to always stay above your keep threshold even if it costs
+more money to do so.
+
+The default is 0.5 - this is the recommended setting.
+
 **input_number.predbat_best_soc_min** (_expert mode_) sets the minimum charge level (in kWh) for charging during each slot and the
 minimum force export level also (set to 0 if you want to skip some slots).
 If you set this to a non-zero value you will need to use the low rate threshold to control which slots you charge from or you may charge all the time.