101Leafy researched the games.
Full Generator

A Thunder Sac gives this a Thunder element. The tradeoff is size. Shelling Lv3
| Class | Gunlance |
|---|---|
| Rarity | 9 |
| Attack | 529 |
| Thunder | 220 |
| Slots | 1 |
| Price | 85,000z |
Upgrades
| Upgraded from | Full Voltage |
|---|---|
| Upgrades into | High Volt Gunlance |
Upgrade tree from モンスターハンターポータブル 2nd G 公式ガイドブック (Enterbrain, 2008), page 760.