Now, for a bit of basics before you get into mobile weapons. You have five values to reflect the abilities of your mobile weapon which are listed below.
Payload = Number of Weapons your Suit can Equip. Beam weapons not covered by this,
Power = Melee Dmg and how many beam weapons you can have equipped.
Armor = Reduces Damage by 2 per point. Goes down everytime your threshold is surpassed.
Speed = The amount of squares your mobile weapon can move on a regular move action. You may also not exceed your mobile weapon's speed in reaction cap while piloting your mobile weapon.
System = How many electronic systems you can have equipped. This also covers equipment hardpoints for things that are not weapons. Additional Sensors, Shields, Ammo Racks,etc.
Mobile weapons, gain passive experience with use (10% of gains acquired through use of the mobile weapon, of a total rather than per encounter), which gain you upgrade levels. The base experience for a upgrade level is way is 50 xp, with a scale of 25 (So second stat is 75, third is 100 and so on)
Upgrading your mobile weapon's stats causes it to get the custom flag - which basically means its no longer equal to the base model it was, you can also change how it looks. To upgrade a suit’s stats you must pay 10% of its base model cost each time. When you upgrade your suit it also gets +5 hp.
This experience is not completely unique, you retain the experience earned in with all suits of that model, just need to do the credits adjustment for it. (You could have like 4 Zaku Is but have 5 levels of upgrades for all of them after you pay the money cost.)
A mobile weapon normally has five upgrade levels.